scan_base64 - decode base64 encoded data

       scan_base64  decodes  base64  encoded  data from src into dest.  It will stop when it encounters any non-
       valid input characters.  It will then write the number of decoded bytes in dest into *destlen, and return
       the number of bytes decoded from src.

       Note that real world base64 encoded data is sometimes permitted to contain whitespace characters  or  new
       lines. This function will not allow those and return the decoded data until then.

       Many  base64  variants  demand  padding  in  the last block. Some don't. This implementation will consume
       padding if it is there, but will not complain if it is not.

       dest can be NULL. destlen can be NULL. dest can be src.

       scan_base64("Zm5vcmQ=",buf,&i) -> return 8, i=5, buf="fnord"

       scan_base64 - decode base64 encoded data

       scan_base64 returns the number of bytes successfully scanned and processed from src.

scan_base64url(3), scan_xlong(3), scan_8long(3), fmt_ulong(3)

                                                                                                  scan_base64(3)

#include<libowfat/textcode.h>

       size_t scan_base64(const char *src,char *dest,size_t* destlen);